The invention relates to the field of insulated pipelines, and in particular to the field of subsea pipelines suitable for use in deep water.
The resistance to flow of liquid products such as oil increases as temperature decreases. This problem can be reduced by using thermally insulated pipelines. However, for offshore pipelines it has usually been more cost effective to reduce the need for insulation by injecting various chemicals into the product.
However, more and more oil and gas is being recovered in deeper, colder water, from subsea production systems where use of viscosity reducing chemicals requires a dedicated line to transport them to the wellhead. This, combined with the fact that the cost of insulating pipelines typically increases with depth, indicates that insulated pipelines are most expensive where the alternatives are least attractive.
Prior art insulation used in undersea pipelines include porous plastic foam, such as polyurethane foam. As known, the lower the density of this insulating material, the higher percentage of air within the material, and therefore the more efficient it is as an insulator. However, as the insulating ability of the material increases due to decreased density, the weaker the material becomes. Specifically, as the density decreases so does the depth at which the foam cellular structure can operate in. Generally, prior wait insulators fail in a few hundred feet of water due to the hydrostatic pressure on the insulation. So the design tradeoff comes down to how light an insulator can be placed onto the surface of the pipe and have it withstand the hydrostatic pressure and other stresses, and at the same time provide the necessary thermal insulation for a long period of time.
These prior art insulators worked in the past because the operational depth of the pipeline was rather shallow. However, the oil industry has undergone a vary rapid movement into deeper water. Several years ago the deepest producing oil well was in approximately fifteen hundred feet of water. The deepest oil well producing today is in four thousand feet of water. The deepest producing oil well planned for two years from today is in ten thousand feet of water. Significantly, as the operating depth increases these relatively lightweight, low cost, low strength prior art materials become unsuitable. Specifically, the materials can no longer withstand the hydrostatic pressure and become saturated with water, thus undesirably becoming a thermal conductor rather than an insulator.
The use of syntactic foams has been discussed as an insulator suitable for deep-sea pipeline insulation. As known, syntactic foams are composite materials in which hollow structures, such as microspheres are dispersed in a resin matrix. However, in any practical manufacturing situation microspheres can not be introduced into the foam in a sufficient quantity to provide the requisite thermal insulation. In addition, the resin binders which hold the microspheres in conventional syntactic foams are too rigid to sustain the bending associated with conventional pipeline laying techniques.
Therefore, there is a need for an insulator which provides sufficient insulation for deep sea operation, and yet is flexible enough to withstand the bending associated with pipe laying operations.